Slice bread into 1/3-inch (1 cm) thick rounds. Toast until golden. Set aside.
Sauté onions and garlic in butter at medium-high for 1 minute. Add mushrooms. Cook 7 minutes, stirring occasionally. Remove from heat.
Stir in cream, rosemary and seasoning. Stir in cheeses. Spread toast with a spoonful of mushroom mixture.
Set on baking sheet and broil until hot—2-3 minutes. Garnish with a few whole pink peppercorns and rosemary. Serve immediately